1. A Quantum Mechanical Progression of Understanding
Hydrogen the atom (1 p+, 1 e-)
modifications
A Quantum Mechanical Progression of Understanding
…Zeff and hydrogen-like orbitals
Poly-electronic atoms (more than 1 p+ and more than 1 e-)
Molecules comprised of atoms (the overlap of e-’s in atomic orbitals…the localized electron model)
…resonance / hybridization
Molecules from a holistic perspective (more than one nucleus and more than one electron)
…molecular orbitals

2. The simplest molecule... H2 1s 1s

3. Constructive Overlap
1sA sB
electron densities add together

4. Destructive Overlap
1sA - 1sB
electron densities cancel each other

5. Interaction of two atomic orbitals dictates the production of two molecular orbitals….
s1s*
Probability distributions are on either side of nuclei
s1s
Probability distribution is in between the nuclei

6. stable molecule H2 s1s2 s1s* E 1s 1s s1s
# of bonding e-’s - # of antibonding e-’s
Bond Order = 2
s1s*
antibonding M.O. E 1s 1s
s1s
Bond Order
probonding M.O.
= 1
(molecular orbital configuration notation) H2
s1s2

7. not a stable molecule He2 s1s* E 1s 1s s1s = 0 Bond Order antibonding
probonding
= 0
He2

8. Factors which influence the strength of the interactions between two atomic orbitals which produce 2 molecular orbitals is determined by:
A. the energy difference between the orbitals.
B. the magnitude of their overlap.
In general…for the interaction to be strong…the energies of the orbitals must be ~ equal and the overlap should be large.
Li2
Liatom 1s22s1
Liatom 1s22s1

9. stable molecule Li2 s1s2 s1s*2 s2s2 E Liatom 1s22s1 Liatom 1s22s1 s2s*
Bond Order 1s 1s
= 1
s1s
Li2
Liatom 1s22s1
Liatom 1s22s1